Cryogenic cables such as a superconducting cable are cooled down by a refrigerant such as liquid nitrogen or liquid helium. As a circulation cooling system for such cables, a system described in Japanese Patent Laying-Open No. 8-148044 is known, for example. In this circulation cooling system, a circulation circuit of the refrigerant is a closed circuit and the refrigerant can be circulated in the state where the refrigerant is not vaporized.
FIG. 2 schematically shows the system. The system includes a reserver unit 30 that stores a refrigerant 33, a pressure-feed pump 31 that pressure-feeds refrigerant 33, a pressure control device 36 that keeps a predetermined pressure within reserver unit 30, a heat exchange unit 32 that cools down refrigerant 33 to a predetermined temperature, a valve unit 34 that splits refrigerant 33 into a cable 35 (three cables exist and each cable is not shown) and the like.
The system repeats the cycle in which refrigerant 33 sent from reserver unit 30 is cooled down to the predetermined temperature at heat exchange unit 32 and is supplied to cable 35 and then returned to reserver unit 30.
Patent Document 1: Japanese Patent Laying-Open No. 8-148044 (Claims and FIG. 1)